Coral Reef Conservation…with Bubbles?

Australia’s most recognized landmark, the Great Barrier Reef, is in danger of being wiped out by coastal human development, which continues to pollute the ocean with carbon dioxide emissions. Coral reefs aren’t just important to humans for their natural beauty and amazing underwater tourism opportunities. They provide vital nutrition and protection for sea life, that humans living in tropical communities rely on to provide basic sustenance. Additionally, coral reefs protect humans from tsunami-like conditions, since they can quell the waves following a storm surge. When large, tsunami-like waves originate in the ocean and move toward the land, large reefs can break the waves and dissipate the waves’ energy. Humans, therefore, have a vested interest in protecting large coral reef communities and reversing the damage of increased ocean acidity.

In March 2016, conservationists received some welcome but surprising news: there is promising technology that would protect our coral reefs and reverse some of the damage already done to them. The technology in question? Bubbles.

Research published by Stanford scientists in Environmental Science and Technology concluded that the way to save the coral reefs is to blow tiny bubbles through the sea water, which will then strip the CO2 from the ocean and release it into the atmosphere. According to the study, between 30 and 60 percent of the worldwide coral reef population has died since the Industrial Revolution, when human carbon dioxide emissions began to increase to unprecedented levels, leading to ocean acidification. The issue with ocean acidification is that it affects the development of organisms with calcium carbonate skeletons, like coral. David Koweek, the study’s lead author, noted that when the ocean becomes more acidified, coral starts to erode since it cannot calcify. The carbonate anion, which is a component of calcium carbonate, exists in equilibrium as both a dissolved and undissolved form in the ocean. Coral reefs extract the dissolved carbonate anion from the ocean, and then synthesize calcium carbonate to further grow and expand the reef. However, when the concentration of carbon dioxide in the ocean increases, the carbonate anion equilibrium condition changes, and the level of dissolved carbonate anion decreases while the undissolved anion level increases. With a lower concentration of dissolved carbonate anion in the ocean, coral cannot calcify as much as before, leading to slower growth in some reefs and negative growth in others. Specifically, some coral populations are shrinking in size and may disappear.

To solve this concerning problem, Koweek and his colleagues hypothesized that if carbon dioxide in the seawater was removed, the coral would be able to re-calcify and grow over time, hopefully back to original levels. Koweek first observed carbon dioxide levels in the ocean during different times of the day, and found that when the sun is out, coral reefs and other marine plant life absorb carbon dioxide for photosynthesis. Once the sun sets, photosynthesis stops, and carbon dioxide remains trapped in the ocean. Koweek concluded that during the evening, it would be optimal to remove the excess carbon dioxide.

The unique solution to this problem involves the use of bubbles, specifically bubbles containing a low concentration of carbon dioxide. According to the laws governing diffusion, if the concentration of carbon dioxide within the bubbles is lower than the concentration in the seawater, the carbon dioxide in the seawater will diffuse into the bubbles. In fact, when the researchers generated bubbles in a tank with a high concentration of carbon dioxide, they were able to increase the natural transfer rate of carbon dioxide from the water to the atmosphere by a factor of 10 to 30.

In fact, when the researchers generated bubbles in a tank with a high concentration of carbon dioxide, they were able to increase the natural transfer rate of carbon dioxide from the water to the atmosphere by a factor of 10 to 30.

Now of course, the first drawback that comes to mind is: Wouldn’t releasing more carbon dioxide into the atmosphere run counter to growing calls for reducing CO2 emissions? Well, yes, but Koweek notes that while more CO2 would be entering the atmosphere, the amount would be miniscule compared to current industrial and commercial output. Koweek continues that the added CO2 would negligibly affect atmospheric conditions, and stronger, healthier coral reefs could make coastal communities safer. In fact, these “bubblers” could be operated using solar energy or other alternative energy sources.

The simple solution of using “bubblers,” is not only a clean solution; it is also something that can be done on all scales, from small ponds to large barrier reefs. Rob Dunbar, a Stanford Earth scientist who worked with Koweek, notes that with “bubblers,” it would be possible to return coral reefs to the state they were in 100 years ago. Scientists have also begun to apply these “bubblers” to revive life forms in the most inhospitable areas on our planet, such as deep in the Baltic Sea, in order to reverse centuries of human pollution and threats from invasive species, like algae. In the future, these “bubblers” could become ubiquitous in coastal areas the world over, ensuring the preservation of marine life and ecosystems for generations to come.